1. Field of the Invention
The present invention relates to a method for freezing perishable foods, and more particularly to a freezing method for preserving animal meats, fish and shellfish, vegetables, and other processed foods for a long time in a fresh state.
2. Prior Art
As a freezing method for foods, there has been known a liquid immersion method. In this method foods are immersed in brine (non-freezing liquid) and because of close contact between the brine and food a high degree of freezing can be obtained.
Freezing is intended to establish a state wherein the texture of the food is barely effected and physical damage arising from concentrated compositions of ice crystals is prevented. Thus, freezing is done in order to prevent drips and the degeneration of the protein which might change the quality of the food during cold storage. Accordingly, the basic requirement is to freeze food as quickly as possible to keep the final temperature as low as practicable and to keep the cooling medium and food to be frozen in as close contact with each other as possible.
In this respect, the liquid immersion method is a good freezing process, and the present inventor has attempted to improve brine according to such a theory.
However, the conventional liquid immersion method has a disadvantage in that the ice crystals grow at the central portion of the food. In particular, one thick ice crystal extends from the central portion of the food toward the surface, and the texture at the center is undesirably damaged and consequently the quality of the food deteriorates. Although the mechanism of this phenomenon is unclear, the state thereof seems as if the textures were broken off from the central portion toward the surface. It is thus considered that the food is rapidly frozen from the entire surface to produce a strain due to the freezing at the center. When such strain reaches the limit, the texture is finally broken down.
As described above, according to the liquid immersion method the food is damaged at the central portion due to rapid freezing from the entire surface. The above defect has still a more serious effect in the crogenic liquid method which employs a liquified gas having an extremely low boiling point.